Electrogasdynamic systems and methods

ABSTRACT

Electrogasdynamic systems in which a plurality of slender gas flow channels carry electrical charges to a downstream charge collector. Each flow channel is of elongate cross section, and the elongate dimension thereof may progressively increase from one end of the channel to the other. Electrical charges are injected into the flow by a corona discharge established in the flow between attractor and corona discharge electrodes extending laterally across the flow in the direction of elongation of the channel cross section and located preferably at the channel side. Adjacent channels are defined by spaced dielectric plates or by spaced rows of conductive wires mutually spaced in the direction of flow and connected externally to an electrical biasing or current-carrying circuit.

6 1 l) *1 3 S R FIP'SSQZ GR 31 582169 1 I i mted States Patent 1 13582594 [72] Inventor Meredith C. Gourdlne 2,085,735 7/1937 Brion et al.55/137 5 West 0rangc,N..l. 3,054,553 9/1962 White 230/69 1211 Appl. No.835,209 3,212,878 10/1965 Bouteille 75/9 [22] Filed June 20,19693,400,513 9/1968 Boll 55/103 [45] Patented JIIDC l, 197] 1 g fi rggg filmrwnwd 204,361 9/1923 Great Britain 55/138 conuuuamnhmm of lppuuuon SenN0. 629,665 10/1961 Canada 55/138 601,270 Nov. 15, 1966 now abandoned848,687 9/1960 Great Britain 310/10 Which in turn is acontinuation-in-part of Primary Examiner-D. X. Sliney application Ser.No. 512,083, now Attorney-Brumbaugh, Graves, Donohue 8L Raymond labandoned.

[54] ELECTROGASDYNAMIC SYSTEMS AND ABSTRACT: Electrogasdynamic systemsin which a plurality i METHODS of slender gas flow channels carryelectrical charges to a 63 Chins, "Dnwhg as. downstream chargecollector. Each flow channel is of elongate cross section, and theelongate dimension thereof may U.S. rogre sively increase from one endof the channel to the 55/122 55/138 other Electrical charges areinjected into the flow by a corona ll. discharge in the flow betweenattractor and of orona di harge electrodes extending laterally acrossthe T 55/133 101v l3, 128-33; 317/103 flow in the direction ofelongation of the channel cross section and located preferably at thechannel side. Adjacent channels [56] References cued are defined byspaced dielectric plates or by spaced rows of UNITED STATES PATENTSconductive wires mutually spaced in the direction of flow and 2,004,3526/1935 Simon 310/6 connected externally to an electrical biasing orcurrent-carry- 2,008,246 7/1935 Deutsch 55/123X ing circuit.

PATENTEDJUN 112m 3582.694

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MEREDITH C. GOURDINE his ATTORNEYS PATENTED JUN 1 I97! SHEET BF 6 Jwwwwmmnmmumm 4%ZI, wk .04

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IN VEN 'l'()l MEREDITH C. GOURDINE his 47 7 0 NEYS ELECTROGASDYNAMICSYSTEMS AND METHODS CROSS-REFERENCES TO RELATED APPLICATIONS This acontinuation-in-part of my copending application Ser. No. 60l,270 forElectrogasdynamic Systems and Methods," filed Nov. l5, i966, which, inturn, is a continuation-in-part of application Ser. No. 5l2,083 forElectrogasdynamic Systems, filed Dec. 7, I965, both now abancloned.

BACKGROU N D OF THE INVENTION This invention relates to improvedelectrogasdynamic methods, systems and apparatus operating on a streamor streams of fluid to effect a conversion between electrical energy andthe energies of the stream, or to effect precipitation of particulatematter entrained in the fluid stream.

In using electrogasdynamic prinicples to derive electrical energy fromthe kinetic, the converter and thermal energies of a stream of fluid or,conversely, to increase the total energy of the fluid stream by applyingelectrical energy to the system, it is highly desirable, ifnotnecessary, to restrict friction losses to a minimum. Inelectrogasdynamic converters, the friction generated as the fluid flowsthrough the converter channel must be considered for two importantreasons. First, friction loss is a measure of conversion efficiency andusually cannot be recouped or preserved for utilization elsewhere.Second, heat energy produced by friction may necessitate cooling of theconverter in order to prevent excess temperatures from damaging theconverter structure, or in order to aid conversion efficiency bycontrolling the fluid temperature so that conversion takes place nearlyisentropically. It is, therefore, preferable to locate the fluidionizing and ion collection electrodes at the side of the converter flowchannel to reduce friction.

In my copending application, Ser. No. 389,360, filed Aug. 13, 1964, anumber of electrogasdynamic converter configurations employingelectrodes at the side of the fluid flow channel is disclosed. Certainaspects of this invention relate to or carry forward the teachings ofthat copending application. In this connection, the present inventionprovides an improved electrogasdynamic converter characterized by highconversion efficiency, better power density (i.e., higher power outputper unit volume of converting apparatus), and a simplified physicaldesign which lends itself well to economic manufacturing methods.

In general, the above improvements are realized by employing a flowchannel of generally elongate cross section which may progressivelyincrease in area in the direction of fluid flow such that the fluidvelocity in the converter is maintained at a low value. Conveniently,the cross section of the channels may be rectangular. Under subsonicflow conditions in the converter channel, the force exerted on theionized fluid by the longitudinal channel field tends to constrict theflow path and give rise to fluid acceleration. By expanding thecross-sectional area of the channel the tendency of the fluid toaccelerate is counteracted, and the converter can be operated at higherpower densities and better ei'ficiency than are achievable with knownconverters.

In a preferred converter embodiment, the transverse dimension of thechannel is maintained constant throughout its length, only the lateraldimension of the channel expanding. The transverse dimension isconsiderably smaller than in previously proposed converters so that theion concentration in the ionized stream is as high as possible in orderto achieve an optimum electrogasdynamic body force (i.e., the reactionforce between the ionized fluid and the longitudinal field in thechannel) without precipitating dielectric breakdown of the fluid. Theelectrode structure in the converter channel takes the form of an arrayof conductive strips disposed laterally and at the sides of the flowpath. Basically, the electrodes in accordance with a preferred form ofthe present invention are thin film strips of refractory metal orconductive ceramic material superposed on the dielectric interior wallsof the channel. In further embodiments, elongate wires or laminatedstrips, partially embedded in the channel walls, may be utilized.

In further embodiments, the attractor electrodes of an ionizingelectrode pair take the form of flat surfaces which extend axiallyupstream from the end of the channel to form an inlet of greatercross-sectional area (normal to the flow) than the corresponding area ofthe channel downstream from the inlet. In such case the corona, ordischarge, electrode is positioned between the attractor electrodesurfaces. For improved ionization efficiency, apparatus disclosed hereinmay employ a second attractor electrode disposed relative to the coronaelectrode to effectively increase the axial dimension of the ionizingfield set up by the ionizing electrode pair.

In accordance with another aspect of the invention, a plurality ofslender channels of the type described above are employed, eachproviding a parallel flow path for the fluid. In this embodiment,adjacent channels share a common boundary structure, which may be in theform of a substantially flat dielectric plate or a row of spacedconductive wires which serve to shield other channels from inducedelectrostatic fields. By multichanneling in this manner, the overalllength of the converter is substantially reduced and construction isappreciably simpler and less costly than for any electrogasdynamicconverter configurations suggested by the prior art, and adequateelectrostatic shielding by electrodes or passive conductors allows alarge number of parallel channels to be used. When this structure isincorporated into precipitator systems, optimum charge densities can berealized by exhausting the fluid streams into a chamber which is greaterin area, normal to the direction of fluid flow, than the combined areasof the channels.

In a related area, the invention also deals with an improvedprecipitator in which the collecting chamber downstream of the ionizingand dielectric generator sections is provided with an electricallyisolated conductor disposed at the interior thereof axially of the flowpath. This conductor attains a potential approximating the potential dueto the space charge field adjacent the upstream end of the conductor tothereby supplement the transverse electrical gradient throughout thelength of the collecting chamber.

For a better understanding of these and other aspects of the invention,as well as the objects and advantages thereof, reference may be made tothe following detailed description and to the drawings, in which:

FIG. I is a plan view of an electrogasdynamic converter in accordancewith the invention, showing, in addition, electrical connections to thevarious electrodes;

FIG. IA is a longitudinal cross section of the converter taken along thelines A-A of FIG. 1;

FIG. 1B is an end view of the converter shown in FIG. 1;

FIG. 2 is a cross section of a modified form of the converter shown inFIG. 1;

FIG. 3 is a perspective partial view showing a corona discharge andattractor electrode configuration suitable for use in the presentinvention;

FIG. 3A is a perspective partial view of another type of coronadischarge electrode in accordance with the invention;

FIG. 3B is a perspective partial view of a further embodiment of coronaelectrode embraced by the invention;

FIG. 3C is a cross section view of the electrode pair shown in FIG. 3,schematically illustrating the shape of a corona discharge ionizingfield in the flow channel;

FIG. 4 is a cross-sectional view of a converter channel constructed inaccordance with the invention, showing schematically electricalconnections for operating the successive stages of the converter channelin series;

FIG. 5 is a cross-sectional view of a converter channel constructed inaccordance with the invention, showing schematically electricalconnections for parallel operations of successive electrogasdynamicstages;

FIG. 6 is a cross-sectional view of a further embodiment of theinvention, employing electrostatic shielding conductors to define aplurality of electrogasdynamic channels;

FIG. 6A is a schematic representation of a portion of the FIG. 6embodiment helpful in explaining the operation thereof;

FIG. 7 is an elevational view in cross section of an electrogasdynamicprecipitation device, employing an improved ionizer construction inaccordance with the invention;

FIG. 7A is a cross-sectional view of the apparatus in FIG. 7, takengenerally along the line A-A;

FIG. 7B is a plan view of the apparatus shown in FIG. 7, taken generallyalong the line 8-8 in FIG. 7;

FIG. 8 is a cross-sectional view of an electrogasdynamic converterchannel in accordance with the invention, employing a second attractorelectrode for increasing ionization efficiency;

FIG. 9 is a partial cross-sectional view of an alternateelectrogasdynamic ionizer suitable for use in electrogasdynamic devicesaccording to the invention.

FIG. 1 illustrates a basic electrogasdynamic (EGD) multichannelconverter in accordance with this invention. As shown in FIGS. 1 through18, the converter includes a number of substantially parallel flatplates 12, spaced apart in a fluid guide or casing 14 to divide theworking fluid flow into several parallel flow paths 13. The plates 12may be structurally supported by suitable spacers (not shown) disposedbetween the plates and elongated in the direction of fluid flow. Thedirection of fluid flow along the axis of this converter is from left toright, as indicated by the arrows. The plates or channel walls 12, aswell as the casing 14, are constructed from a dielectric material suchas magnesia, alumina, or boron nitride for higher temperature gases ormylar, lucite, or stycast for low temperature gases. As will bediscussed further, the plates 12 may be made from other than dielectricmaterials which are coated with a dielectric film or sufficientthickness to preclude breakdown under operation conditions in therespective flow paths.

In accordance with the invention, each of the plates 12 in the converteris fan-shaped, i.e., expands from a width w, at the upstream end orinlet 15 of the converter to a width w at the downstream end or outlet16. The casing itself is of generally rectangular cross section, so thatthe cross section of each individual flow path, or channel 13, is alsogenerally rectangular throughout its length. Disposed laterally of andat the sides of the respective flow paths 13 are corona dischargeelectrodes 18 and attractor electrodes 20 situated so as to besubstantially flush with the surfaces of the dielectric plates or walls12. The attractor electrodes 20 have flat surfaces exposed to theinterior of the flow paths 13, whereas the corona electrodes 18 comprisea plurality ofsharp, laterally extending parallel edges from which acorona discharge (see FIG. 3C) occurs when a high potential gradient isimpressed between the attractor and corona electrodes. A more detaileddescription of electrode structure will be found in the discussionassociated with FIGS. 3-3C. Each plate 12 includes a series of suchelectrodes, either the corona discharge electrodes 18 or the attractorelectrodes 20 (or as discussed later, a combina tion of both) beingspaced apart along one side of channel 13 in the direction of fluidflow. In the converter shown in FIGS. 1-18, the first and alternateplates 12 thereafter include six attractor electrodes 20, theintermediate plates 12 containing six corona electrodes 18 in opposedrelation to the attractor electrodes 20.

Each attractor electrode 20 and the corona discharge electrode 18immediately adjacent it comprise a fluid ionizing electrode pair which,when a sufficiently high electric potential is applied thereto, providesan ionization field which ionizes the stream of fluid in the flow paths13 defined between the respective plates 12. It is seen that consecutiveflow paths 13 share a common electrode in each instance. For example,the corona discharge electrode 18 in the second of the plates 12 iscommon to the top flow path and the flow path immediately below it. Eachelectrode pair and the downstream portion of the channel defined betweenadjacent plates 12 may be referred to as an EGD stage, the length ofthestage being the distance along the flow path between consecutiveelectrode pairs.

At the downstream end 16 of the converter, each flow path has associatedtherewith a collector electrode 22 which also extends laterally of theflow path. As in the case of the corona discharge and attractorelectrodes, the collector electrodes 22 are substantially flush with theplates 12 at the sides of the flow paths 13. The collector electrodes 22are similar in construction to the corona electrodes 18 in that eachprovides one or more sharp edges exposed to the flow path. As will beexplained later, however, the function ofthe collector electrodes 22differs from that of the corona electrodes 18.

The spacing between the plates 12 in a typical converter may be aslittle as l millimeter; closer electrode spacing renders it difficult toachieve corona discharge in the converter channels without precipitatingelectric arcing between electrodes. A preferred range of spacing isbetween approximately 1 millimeter and 5 millimeters, the latterdimension being still small enough to promote good ionization. In thisconnection, an additional feature of the very thin converter channel isthat considerably smaller ionization potentials can be used to excitethe electrodes. Spacings as large as l inch may be used for specialapplications.

FIG. 2 illustrates an alternate form of the FIG. I converter, in whichthe dielectric plates have been replaced with flowsplitting layers 24 ofdielectric wirelike elements 24a. As shown, the elements 24 extendlaterally of the flow paths [3 and are generally parallel to the coronaand attractor electrodes 18, 20. The attractor electrodes 20 aregenerally of the same construction as those in FIGS. l-lB, but thecorona electrodes 18 in this embodiment are conductive wires. Theelements 24a may be, for example, wires such as the corona electrode 18coated with a refractory dielectric material (e.g., alumina) and areclosely spaced (not necessarily touching) along the converter axis.Although the physical surfaces" of the layers 24 are not flat, as is thecase with the dielectric plates 12 in FIG. 1, the surface irregularitydoes not appreciably increase friction losses in the flow path. This isdue to the thin boundary layer of flu d established immediately adjacentthe surfaces of the layers 24 under subsonic flow conditions, whichpresents a substantially smooth boundary configuration to the fluidstream. The advantage of this construction is its adaptability toeconomical mass production.

The wires extend through the sides of the channels (not shown) andconnect externally to a circuit providing a reference potential on thewires, and therefore at the sides of the channels. The function of suchwires and their external connections are more fully explained inconnection with the description of FIG. 6.

ELECTRODE CONFIGURATION FIGS. 3 through 3B illustrate a number ofpreferred electrode configurations which are suitable for use in EGDconverters in accordance with the invention. In FIG. 3, the attractorelectrode consists of a thin film strip 25 of conductive materialsuperposed directly on the surfaces 26a of a dielectric wall 26 of theEGD channel. The corona electrode comprises a series of generallyparallel, narrow, elongate conductive strips 27 formed on the surface290 of the opposite channel wall 29. The width of this strip issufficiently narrow to present to the flow path a line of coronadischarge, i.e., a narrow geometric configuration which freely emitscharged particles into the flow path when an ionizing potential isconnected between it and the attractor electrode stripe 25. Thethicknesses of the stripe 25 and the very narrow corona stripe 27 aredetermined by the conductivity of a material used and the amount ofcurrent which the electrode must carry. If the electrode thicknessbecomes excessive, the electrodes may be recessed into the walls 26 toreduce friction at the side of the fluid flow path.

The attractor and corona electrodes of FIG. 3 can be formed by thin filmdepositi: n techniques or by spray coating the channel wall surfaceswttn a conductive material. One of the problems previously encounteredwith refractory material electrodes is their susceptibility to extremeoxidation which effectively coats the electrode surfaces with adielectric layer which eventually precludes corona conduction betweenthe corona and attractor electrodes. Certain ceramic materials, however,such as titanium diboride and zirconium diboride have sufficiently highconductivity at converter operation temperatures (e.g., in excess ofi000 K.) and yet, because they are ceramic, are not sub ect to surfaceoxidation. Other such materials having the same general characteristicconductivity and suitable for use in electrodes are zirconium carbide,boron carbide, titanium carbide, and vanadium carbide. The walls orplates of the flow channel are preferably dielectric throughout;however, it is possible to achieve good results also by coating thechannel walls with dielectric material. High conductivity ceramicmaterials such as those noted above may be applied to dielectricmaterials (e.g., alumina or boron nitride) by spray coating, thuspermitting rapid and economic formation of the electrodes. A foremostadvantage of clec trodes constructed from thin film conductive materialis that, in conjunction with the expanding channel, the overall lateraland axial dimensions of the converter are reduced while, at the sametime, high isentropic efficiency is preserved.

FIGS. 3A and 3B show alternate forms of electrode construction. In FIG.3A, the attractor electrode 31 is a single bar of conductive materiallaminated in the EGD channel wall 26. The corona electrode comprises aplurality of flat laminated strips 32. interposed between dielectricsections 33 and disposed transversely of the wall 29. The strips 32 havesharp edges 320 which are substantially flush with the channel wallsurfaces 29a for exposure to the fluid flow and present a line of coronadischarge thereto. in FIG. 3B, the corona electrode comprises severalparallel thin wires 34 which may be at least partially embedded ingrooves 35 in the channel wall 29. Any of the above electrode formsprovide satisfactory and efficient fluid ionization and lend themselveswell to mass production manufacturing.

FIG. 3C illustrates the approximate shape of the corona discharge field37 under the influence of fluid flow between the electrodes of the typejust described. As shown, when an ionizing potential, represented by thebattery 39, is impressed across the corona and attractor electrodes 39,40, an electric field extends transversely of the flow channel in whichions 42 are produced and carried downstream by the fluid. Although thecorona electrode shown comprises only three conductive strips 39, it isunderstood that higher corona discharge densities in the electric field37 may be obtained by employing additional such strips, closely spaced.

Returning to FIG. 1, representative electrical connections to theconverter are shown. A voltage dividing network 44 is connected betweenthe corona discharge electrodes 18 of the first stages and therespective collector electrodes 22 which are also electrically coupledtogether, as shown in FIG. 1A. ln keeping with the desirability ofcompactness and higher power output per unit of converter volume, thevoltage divider 44 is a thin film stripe of resistive materialsuperposed on an outside surface 45 of the casing. The film may beeither a refractory metal or conductive ceramic material such aszirconium diboride. For purpose of illustration, a load 44a is shownconnected across the converter output, in parallel with the voltagedivider network 44. The attractor electrodes and the corona dischargeelectrodes 18 of the following stages are similarly electricallyconnected together, as best observed in FIG. LA, by the conductors 46and 48, respectively. A voltage source 49 is connected via a switch 490to the first or upstream ionizing electrode pairs. The attractorelectrodes of the following stages are connected to taps 50 on thevoltage dividing network 44 by the conductors 46a46e which terminate onadjustable contacts 51. The taps 50 are preferably located on thenetwork 44 so that the axial field E, created in the channel when theconverter is operating is substantially linear.

The positionable contacts 51 on the voltage divider network 44 providemeans by which the potential applied to the respective pairs of ionizingelectrodes may be set to obtain the correct ionization voltage for eachEGD stage. lt is, of course,

desirable that all of the ions (positive or negative) injected orcreated by ionization at the first EGD stages arrive at the collectorelectrodes 22. However, owing to the space-charge-induced fields in therespective flow paths 13, the ions experience an electrostatic forcewhich tends to drive them to the sides (plates 12) of the EGD channel.The intermediate electrode array, therefore, compensates this depositionof ions by replenishing the fluid stream with ions produced in theionization field. However, by properly adjusting the ionizationpotential, the ion concentration in the fluid stream can be controlledto be in maximum permissible proportion to the fluid density. This, inturn, is accompanied by an EGD body force which is also maximum, andconversion efficiency is therefore optimized. These facts will be betterappreciated in the subsequent theoretical discussion.

OPERATION OF THE ELECTROGASDYNAMIC CHANNEL For purposes of explanation,FIG. 4 illustrates a single EGD channel of the FIG. 1 converter, likeelements being designated by the same numerals used in FIG. 1. In brief,operation of the converter is as follows: A working fluid such as acombustion gas from a source (not shown), flows through the channel fromleft to right, as indicated by the arrows. When the switch 49a isclosed, the corona discharge electrode l8 is biased negatively withrespect to the attractor electrode 20 by the voltage source 49, and acorona discharge field 53 of the type shown in FIG. 3C is establishedbetween these two electrodes, thereby injecting electrons into thestream to form low mobility negative ions 54. Those ions 54 are sweptdownstream by the fluid and travel across the channel under the actionof the space-charge-induced electric field which exists in the channeldue to the presence of charged particles. Some, but not all, of thenegatively charged ions deposited at the side of the channel areneutralized by the attractor electrode 20a; the remainder of thecharge-carrying ions are blown further downstream to subsequentattractor electrodes 20b-20 and the collector electrodes 22. To theextent that the attractor electrodes 20a20e neutralize the chargedeposited at the channel wall 12, they are also collector electrodes.

When negatively charged particles reach the surfaces of the attractorelectrodes 20:: 20e, the negative charge (electrons) finds a paththrough the external voltage divider network 44 to the first coronadischarge electrode 18. This flow of electron current establishes apotential buildup across the voltage divider network 44 which isprogressively more negative at the downstream taps 50. ln this manner,the voltage divider network and the attractor electrode connectionsthereto allow the initiation of EGD conversion by one or more startingpotentials which are considerably less than the steady-state operatingpotential between the electrodes 18 and 22.

With the movable contacts 51 positioned downstream of the respectivetaps 50, each of the corona electrodes l8a-l8e is impressed with avoltage which is negative relative to the associated attractorelectrodes 20a20e, and each electrode pair is biased to sustain anionizing field in each EGD stage. The intermediate electrode pairsl8a20a-l8e20e replenish the negative charge lost by deposition on thesides of the channel and neutralization by the attractor electrodes 20a--20e. Because of the ion reinjection, most of the charge currentinjected into the flow channel by the source 49 finds its way to thecollector electrodes 22 at steady-state conditions. Moreover, with aproper adjustment of the movable contacts 51 on the voltage dividernetwork 44, the ion concentration n in the channel can be controlled sothat it is proportional to the density of the fluid, thereby maintainingthe induced electrostatic (space charge) field at the desired value. Formaximum efficiency, this field is kept to a value very close to thebreakdown voltage E, of the ambient medium (e.g., air) surrounding theconverter.

Owing to the increasingly negative potential of downstream electrodepairs, ions forced through the channel by the fluid gain electricpotential energy. since work must be exerted on the negative ions 54 inovercoming the repelling longitudinal field E, existing in the channelThis work is supplied from the kinetic and thermal energies of thefluid. Thus, energy is extracted from the fluid and converted intoelectrical energy. The negative charge neutralized by a collectorelectrode 22 takes parallel paths-one through the voltage dividernetwork 44 to provide a bias potential across the last electrode pairl8e 20, and the other through the high impedance load 440 where theelectrical energy is utilized.

As previously noted, the corona and collector electrodes differ infunction although they are similarly constructed. The collectorelectrode 22 "collects" or neutralizes the negative ions 54 by, ineffect, emitting positive ions, whereas the corona electrodes 18a-l8eionize the fluid by an emitting negative charge. If the polarity of thevoltage applied to the ionizing electrodes were reversed, the same wouldhold true, except that the corona electrodes would then emit positivecharges and the collector electrode negative charges.

It should be noted that the conversion process just described isreversible. That is, if a high voltage source of the polarity shown weresubstituted for the load 44a and the connections to the electrodesreversed so that positive ions would be injected into the fluid stream,the EGD converter acts as a fluid pump whereby the fluid is acceleratedthrough or compressed in the channel. In this case, the "body force" isthe attractive force exerted on the fluid by the longitudinal field E,,Ions collide with fluid particles as they travel through the channel,bringing about a viscous coupling which drags the fluid toward thecollector electrodes 22.

In FIG. 4, the electrical connections to external circuitry are suchthat successive stages of the EGD channel (each stage including onecorona and attractor electrode and the downstream length of the channelto the next electrode pair) is in series; that is, the charge carryingions viscously coupled with the fluid increasingly gain potential energyas they are propelled downstream to the collector electrodes 22. HO. 5,on the other hand, depicts a single EGD channel connected for paralleloperation so that the output current, but not the voltage betweensuccessive stages, increases as the chargecarrying particles are carrieddownstream. In this channel, the corona electrodes 56a-56d alternatewith the attractor electrodes 5812-5811 at each side of the channel.Thus, the attrac tor electrode 580 of the first electrode pair is in theupper plate 60; in the following electrode pair it is in the lower plate62, and so on. As in FIG. 4, the corona electrodes 560-561! are inopposed relation to the attractor electrodes so that the ionizing fieldextends transversely of the channel flow path. Upon closing the switch63, the first and alternate electrode pairs thereafter, 56a-58a and56c58c, are biased by the potential source 64 to yield negative ions 65to the stream. When the switch 66 is closed, a potential from the source67 is applied to the remaining electrode pairs S6b-58b and 56d- -58d.Since, however, the corona electrodes 56b, 56d are positive in potentialrelative to their associated attractor electrodes 58b, 58d, positiveions 69 rather than negative ions are produced.

As the ions are swept downstream by the fluid (flowing from left toright), they move toward the sides of the flow path due to space chargeeffects and intercept the corona discharge or ionization field of thenext stage where they are neutralized by the charge of opposite polarityin that field. lt should be noted that in this configuration, theelectrodes 56a56d are both collector and corona electrodes. That is.when a negatively charged particle 65 arrives at the longitudinalposition of, for example, the electrode 56b, it is neutralized by theemission of a positive charge 69 from that electrode and passes into theexternal load 70. At the same time, however, positive ions 69, insufficient quantity, are continuously created by the positive coronadischarge between the electrodes 56b and 58b so that the charge in thenext EGD stage is constituted of primarily positive ions. This sequenceof events is identical for all stages; if follows that the currents areadditive through the load 70.

Since alternate stages conduct charges of opposite polarity, and sincesuch alternate stages are connected in parallel by the external circuit,they are also in parallel internally, and the voltage generated in onestage is followed by a generated voltage of opposite polarity,relativeto the respective corona electrodes, in the next consecutivestage. This is because in one stage, negative charges are being movedagainst a negative field and in the next stage, positive charges buck apositive field.

By arranging successive stages in parallel as shown in FIG. 5, theelectrical impedance of the EGD generator (or the EGD pump as the casemay be) is reduced. (For operation as a fluid pump or propulsion. amodification of connections similar to those outlined for the FIG. 4circuit is made; viz., the load 70 is replaced by a voltage source andthe polarity of the voltages from either the source 70 or the sources67, 64 reversed.) The minimum voltage per stage is determined bypractical considerations such as minimum electrode size and theirspacing in the same plate. The closer the electrode spacing betweenconsecutive stages, the lesser the generated voltage. It has been foundthat voltages as small as 10,000 volts can be produced at lowerefficiencies, but 50,000 volts per stage is more practicable. W

THEORY AND DESIGN FACTORS It was earlier briefly noted that inconverters in accordance with the present invention, the ionconcentration n can be controlled for optimum converter efficiency. Thatis, the ratio of the EGD body force to the friction force is maximum forany given fluid velocity.

The longitudinal electric field E, is maintained uniform along thechannel by choice of suitable bias resistances in the external voltagedivider network. Preferably, it is maintained at a value that isconvenient to handle in the external circuit; for example, 3X10 voltsper meter which is the breakdown strength of air at standard temperatureand pressure.

The ratio of friction-force ie, the force opposing fluid motion) to theEGD body-force f (ie, the force supplied by the fluid in moving ionsagainst the field E in the case of an EGD generator) is given by therelation where c; is the coefficient of fr ction. p is the fluiddensity, u is the fluid velocity, s is the ptil'l'lltl fi; of freespace, E, is the uniform longitudinal electric field, which ismaintained just below the breakdown strength of the ambient air E,=I;=3X l0 volts/m., and E, is space-charge induced electric field normal tothe walls of the channel. E, is proportional to the ion concentration nin the channel and is limited by the breakdown strength E of the gas,which in turn is proportional to the density p; therefore, let the ionconcentration n be adjusted such that v Eb=Ez;(P/P) where the bardenotes standard pressure and temperature conditions.

With the ionizing electrode circuit adjusted to inject sufficientcurrent to keep the ion concentration n at its maximum allowable value(Expression (2)), it is possible to evaluate Expression (2) under atypical set of subsonic flow conditions. For example, assuming thefollowing conditions:

u=50 m./sec., the friction to body force ratio becomes 1 Cf F112 In thissituation the local isentropic ffiCll1C of the channel IS 1 o f. b (3)This value is relatively high and much larger than achievable with knownconverters. Specifically. the attainment of high efficiency results from(I restricting fluid motion to moderate velocities and (2) reducing thecoefficient of friction through employment of special electrodeconstruction.

It can also be shown by integrating the generalized gasdynamic equationsfor the constant velocity expanding channel that the relationshipbetween an axial position in the channel and Mach number is given by E fi I('Y" "(fI' fb) where x is the distance from the position where sonicconditions would occur, M is the Mach number, y is the specific heatratio, and h is the height (transverse dimension) of the channel.

The cross-sectional area A and the width of the channel w are also foundfrom integration to be related to the Mach number where the asteriskdenotes sonic (M=l conditions.

Since the flow is approximately isentropic, we can write for the othergasdynamic variables the following approximate expressions for Theseformulas are very useful in the design of EGD generators and pumps ofthis type. By way of example, let us assume that we are to design an EGDgenerator having an efficiency of 50 percent, operating on a combustiongas having the following inlet conditions:

M l 0.0745 Using the foregoing gasdynamic formulas (6)( l l the exitconditions after extracting 50 percent of the total enthalpy are:

p,,=2 92 atmospheres it an, Was, (12

where it has been assumed that the ion mobility is FI (1 4 k, m/volt-sec. (13) Thus, in practice, the minimum voltage that can beextracted from a single stage under the above set of conditions is Ifthe ion mobility is higher than this assumed value at standardtemperature and pressure (k,=l0rn'/volt-sec.), then the aspect ratio I/hof a single stage is smaller, more stages are required, and a lowervoltage can be extracted per stage.

Continuing with the above, assuming '1': 1mm., the dimensions of thechannel (see FIG. 1) can be determined from the foregoing expressions.These dimensions are:

h=l0" meters L=3.59 meters I=17 mm.

w =meter w,,=meters.

Each channel, therefore, contains L/I=2l 1 stages and the power outputis 10 watts.

It is additionally significant that the current in each stage is alsoconstant, since it is given by the formula Fen uh w, (15) and the ionconcentration n is proportional to the density p, while the width w ofthe expanding channel is inversely proportional to the density. Itfollows that the power extracted by each stage is also the same.

Because the thickness of each dielectric channel wall or plate can alsobe reduced to as little as I millimeter, l0 megawatts of output powercan be generated by multichanneling the converter with of thesechannels. The total height of the converter channels is thenH=100X0.002=02m. and the total volume occupied by the assembly isapproximately 1.08 m The power density of this assembly is thereforeapproximately 10 watts/m Another very important aspect of this system isthat because of the attainable isentropic efficiency no coolant need beused to restrict fluid temperature and the converter can be used atisolated locations where there is often no available cooling fluid suchas water. Moreover, the converter may operate on any of a number ofgases, including natural sources of wet steam from geothermal streams,to generate commercially distributable power at the situs of naturalenergy sources.

ELECTROSTATIC SHIELDING In describing FIG. 2, it was mentioned that rowsof wires dividing adjacent flow channels may be connected to an externalcircuit to provide on each wire conductor a reference potential. Thesewires, however, have the further important function of establishing areference potential that prohibits formation of excessive electricalfields and potentials at the flow path boundary which might precipitatedielectric breakdown of the gas or channel components and cause damagingarcing. The wire conductors, therefore, also tend to shield each channelfrom space charge potentials and fields induced by other adjacent andnearby channels.

It should be recognized that the space charge field gradient within anenclosure serving as an electrogasdynamic channel is dependent upon thespace charge concentration and the distance over which suchconcentration is present Thus, if several such channels are disposed inclosely ad acent relation, space charge fields in each channel induce aspace charge field in adjacent channels and, absent any other provisionfor interchannel shielding, those space charge fields can be neutralizedor cancelled only by an induced space charge field having an opposingeffect. It is apparent, moreover, that the outer channels in a stack orarray of parallel flow channels, such as that indicated in FIGS. 1-18,tend to operate under a substantially higher transverse space chargefield than those channels at the interior of the array Thus, if eachelectrogasdynamic channel is independently operated near maximumtolerable limits of space charge concentration. it is possible that thebreakdown electric field threshold will be exceeded in at least theouter parallel flow channels.

In addition, the dielectric surfaces of the channels tend to holdelectrical charges contacting them and may acquire a surface chargeconcentration sufficient to precipitate arcing within the channel.

To a certain extent, such adverse effects of induced space charge fieldscan be minimized by, for example, spacing the ionizing electrodes atshort axial distances and biasing axially adjacent electrodes atpotential differences well below critical values. In such case, theionizing electrodes function to provide terminal points for the electricspace charge field, thereby limiting the maximum distance over which anyspace charge concentration can act. This expedient, however, may proveimpractical for long channels, requiring an excessive number ofelectrodes. In FIG. 2, the shielding wire conductors are dielectricallycoated, thereby preventing electrical discharge of any ions or chargedparticles contacting the wires after being driven to the flow boundaryby aerodynamic and space charge effects, but improved results areobtained by employing bare conductive surfaces and using the dielectricproperties of the gas to isolate the channels. The apparatus of FIG. 6incorporates the latter solution to this problem, and carries forwardthe techniques disclosed in my copending application Ser. No. 756,220,filed Aug. 29, I968.

Referring to FIG. 6, a series of parallel electrogasdynarnic conversionchannels are formed between adjacent axial rows of rigid, exposedelectroconductive (e.g., metal) rods 70. Each row of rods may beconsidered a flow boundary for a thin electrogasdynamic channel boundedby an adjacent row of rods. It is not, however, essential that the rodsof each row be so closely spaced as to form a continuous boundary layerfor the establishment of laminar flow, as the device may also beconsidered as a single channel having an array of conductive rodseffective to set up the desired potential distribution, as will beexplained. It should also be remarked that although the rods areconductive, the gas may be considered a dielectric medium such that therods effectively establish a dielectric guide for the flow. For thepurpose of explanation, each electrogasdynamic channel (formed byadjacent rows of rods) is connected to operate in the manner describedin connection with FIG. 5, with each channel shown to contain threestages. The length of each stage is determined by the axial distancebetween the ionizing electrodes 72, 74 of each channel, with the laststage shown terminating in electrodes 76 similar to the attractorelectrodes 72, but functioning as collector electrodes. It should beobserved in this case that a single corona electrode 74 is locatedintermediate and establishes a corona discharge field to each of, twoadjacent attractor electrodes 72.

The entire assembly, including the channel-defining rods 70, theionizing electrodes 72, 74 and supporting structure is housed in asuitable pressure vessel 78, which may assume the diverging shapes ofthe apparatus of FIGS. 1-18 so that the lateral dimension of thechannels progressively increases from one end of the device to theother. The attractor electrodes 72 for the first and third stages areconnected through suitable conductive elements 79 to the metal wall ofthe vessel 78, with the attractor electrodes 72 of the second stage(serving also as the collector electrodes for the first stage), togetherwith the collector electrodes 76, interconnected through insulatedterminals 82 to a high voltage output conductor 84 Gaseous flow throughthe assembly is indicated by the direction of the arrows. The coronaelectrodes are connected to a potential source in the manner shown inFIG. 5. A dielectric coating at the vessel interior isolates the vesselwalls from the charges cam'ed by the flow.

All rods 70 at a common axial location in the channels are connectedthrough conductors 85 to a common point on an external resistive biasingnetwork 86, thereby establishing for all channels a reference potentialwithin the channel, and a maximum potential difference between any ofthe axially spaced rods 70. Preferably, the network constitutes a highresistance film on a sidewall of the fluid guide vessel 78 which, ifdesired, may be grounded, as shown. Connections of the network 86 to therods 70 are then made by physical contact of the rods with the resistivefiim.

With the construction of FIG. 6, the rods serve the dual function ofestablishing within each channel a uniform applied electric field alongthe length of the channel and of neutralizing the interchannel inducedspace charge fields by providing closely spaced terminal points (atselected potentials) for the space charge fields. Any charged particlesor charges striking the rods 70 become discharged, with the chargesbeing conducted through the external biasing network 86. Current throughthe rods 70 is effieientl y utilized in the external circuit 86 tomaintain a desired potential on each rod and thereby also to maintain auniform axial electric field gradient within the flow paths. The use ofbare conductive elements such as the rods 70 also reduces the previouslyexperienced problem of excessive buildup of electrical chargeconcentration at the dielectric boundaries ofthe conversion channels.

It is immediately apparent that maximum effectiveness of the conductiverods 70 in shieicing channels from induced space charge fields fromother channels is obtained by making the spacing between rods as smallas possible. However, this leads to larger, and perhaps inefficient,pressure drop in the channel due to viscous drag. By and large,therefore, optimum spacing of the conductive rods is determined by thespace charge concentratier. within the device and the maximum distanceby which such rods car be spaced without incurring dielectric breakdown.Although the rods 70 in FIG. 6 are shown of circular cros section, othercross-sectional configurations, such as an ellipse, may be used toreduce aerodynamic drag Referral to FIGv 6A may be helpful in betterunderstanding the manner by which the rods 70 limit the maximum spacecharge field in the channels. FIG. 6A shows in cross section a few rods70 at any location in adjacent channels. Each rod 70 is spaced adistance it from the most closely adjacent rod (on a diagonal) so thatthe transverse height of each channel between rows of rods is Theforegoing geometrical arrangement is used for purpose of explanation andease of computation only and should not be taken as critical orpreferred. An arbitrary imaginary enclosure in the form of a square 90may be drawn to surround each rod to designate the boundary in space ofall electrical charges inducing a surface charge on each rod. Theboundary is drawn so that it falls midway between any two rods 70 inorder that the same area is obtained for each enclosed area.

The area .4 of unoccupied space within each square, from inspection,

If the particle concentration in the flow is assumed uniform at N,, witheach particle having n, charges of e (an electronic charge), then thetotal charge Q, per unit length of each volume having an area A is:

By GAuss' Law, an equal image charge appears on the cylindrical surfaceof the rod 70, the area Q, of which is a,.=21rr. The total surfacecharge per unit length is therefore the product of area and surfacecharge density 11, or:

where E, is the electric field at the surface of the rod due to thesurface charge The quantity E, is also equated to the space charge fieldat the rod.

Since Q,=Q for the assumed geometry, expressions (l7) and (18) may beequated;

From expressions (20), it can be seen that the maximum space charge E,at any point in the channel is directly related to the rod (conductor)spacing h. When h is made smaller, the space charge is reduced by acorresponding amount, and as charge concentration en N increases, thespacing h must be made smaller for any given space charge field E,.

An important feature of the embodiment of FIG. 6 is the axiallystaggered location of the conductive rods in adjacent channels. With therods 70 staggered, as shown, the electric field established between anyrod of one row and the closest rod of an adjacent row has both axial andtransverse components. The transverse component of the electric field,however, alternates in polarity from one rod 70 to the next. Acorresponding alternation of the electrostatic force on any particlemoving between any two adjacent rows of rods, therefore, will occur asthe particle moves downstream. This alternation of the electrostaticfield force on the particles tends to keep them within the boundarydefined by the rows of conductors and thereby prevents their tendency todrift out of the respective channels and into the planes of the rods.Fortunately, turbulence and flow separation around the rods tend tocounteract this effect and, therefore, although the staggered array ofrods is preferred, it is not necessary.

in a properly designed channel, where both the axial electric fieldopposing downstream motion of the charges and the maximum space chargefield between adjacent rods are proportional to gas density, it can beshown that the relative current loss to the rods is independent of spacecharge concentration. Moreover, the ratio of friction force toelectrical force on the rods is inversely proportional to density;therefore greater space charge concentration may be used with greatereffectiveness in achieving high isentropic efficiency. This is becauseas space charge concentration increases, friction forces consume a lesssignificant proportion of the total energy expended.

Under typical conditions, the Reynolds number R of flow may beapproximately 10; therefore, it can be predicted that gas flow separatesfrom the rods directly exposed to the gas flow. Accordingly, very fewcharged particles may be expected to diffuse to the downstream profilesurface of the rods. Thus, in general, only the upstream profile surfaceof the rod collects an electrical charge and that charge, if carried bya solid particle, discharges to the rod, removing the attractiveelectrostatic forces tending to hold the particle on the rod. Therefore,the front profile surfaces of the rods tend to remain clean, althoughparticles are observed to collect in the stagnation zone at the rear, ordownstream profile surface of the rod.

in experiments conducted with the type of device shown in FIG, 6,current losses due to precipitation of charges to the bare metal rodswas found to constitute less than 2 percent of the total current carriedby the channel. In these experiments, the spacing between rods was 2cm., the radius of each rod was 5 mm., the length of each channel stagewas 30 cm., the maximum electrical field E, within each channel wasvolts/meter and the gas velocity was 30 meters/sec.

ELECTROGASDYNAMIC PREClPlTATOR IMPROVEMENTS Turning to FIG. 7, there isshown an improved electrogasdynamic precipitator in accordance with theinvention. In principle, this precipitator operates in an identicalmanner to the precipitators disclosed in my copending application Ser.No. 477,5l6, filed Aug. 4, 1965 for "Precipitator Systems," Inaccordance with the present invention, however, the ionizing section ofthe precipitator includes dielectric fluid guide means comprisinggenerally a series of spaced parallel dielectric plates 130 which arecontoured at the upstream and downstream ends to form a converging inlet131 and a diverging outlet 132 between each of the plates 130. Extendingaxially in the upstream direction from the ends of the plates 130 aresubstantially flat conductive plates 1320, with adjacent plates formingbetween them an inlet for each of the flow channels 130a defined betweenadjacent plates 130, As shown, the cross-sectional area of these inletsnormal to the flow path is greater than the correspondingcross-sectional area of the flow path downstream thereof. The plates1320 form attractor electrodes for attracting an ionizing discharge.

Disposed between the attractor electrode plates 1320 are several closelyspaced corona discharge wires 133 arranged in a planar configurationgenerally parallel to the plates 1320. Together, the corona dischargewires 133 and the attractor electrode plates 132a form an ionizingelectrode pair for establishing an ionizing, or discharge, field at theinlets to the respective flow channels 130a when an electrical ionizingpotential source 134 is connected between the attractor and coronaelectrodes, as shown in FIG. 7A.

The entire ionizing and flow channel assembly may be supported in asuitable conduit 136, as best seen in FIG. 7A, which in turn is suitablysecured to the wall of the collecting chamber 138. The corona dischargewires 133 are passed through small holes bored in the sides of thesupporting conduit 136 and held in place by retainers 137 at either endof the corona wires. The supporting conduit 136 may be metal, asdepicted, and one terminal of the ionizing source, here represent by thebattery 134, may be connected directly to the conduit 136, the otherterminal of the source 134 being connected directly to the severalcorona discharge electrodes 133. Located downstream of the dielectricplates is a collecting chamber, or collector electrode, 138.

The collector 138 is preferably constructed from a metallic material andis also preferably (but not necessarily) cylindrical. If desired thecollector surface 138a may be constituted of a dielectric coating toprevent electrical discharge of the particles reaching the collector138. In such case an electrostatic force on the particles tends to holdthem to the surface 138a and thus reduce their reentrainment. It isadditionally desirable to have the cross-sectional area (normal to theflow path) of the collector 138 larger than the combined correspondingcross-sectional areas of the individual flow paths defined between thedielectric plates 130. ln such case, the velocity of the gas entrainingthe particles to be precipitated is decreased, thereby giving theparticles a longer residence time in the collector and enhancing theprobability that the space charge field in the collector will force themto the wall of the collector, where the particles are precipitated. Uponreaching the wall of the collector 138, the particles, if they are heavyenough, are free to gravitationally descend downwardly along thecollector inner surface 138a and out of the precipitator through theannular exit formed between the collector 138 and conduit 136.

From the foregoing, it will be apparent that as the gas containing theundesired particles is flowed through the conduit 136 and into theinlets of the flow channels, the entrained particles become charged bythe ionizing field established between the corona and attractorelectrodes 133 and 1320, respectively, and are carried fartherdownstream by the dynamic forces of the gas stream, guided by the flowchannels 1300. The collector electrode 138 may be connected externallyto ground or, alternatively, through an external load. It

will be further recognized that the dielectric plates I30 isolate thecharge flow from external electrical circuits and form anelectrogasdynamic converter, or generator. section in which thepotential energy of the charged particles is raised at the expense ofthe kinetic energy of the fluid stream, since the stream exerts a forcein pushing the fluid and particle mass downstream against the axialfield existing between the ionizing electrodes 1320, 133 and thecollector electrode 138. This potential energy, of course, appears as aspace charge potential field within the collector section. 7

An additional function of the dielectric converter section of theprecipitator, i.e. the dielectric plates 130, is to direct theelectrical image force between the emitted charges and the flowchannels. Without the dielectric plates 130, every charge emitted fromthe corona electrode would produce an image charge that would remain inthe metallic attractor electrodes. Then the charge released from thecorona electrode, as it began to travel downstream, would set up anintense electrical field between it and the image charge at theattractor electrodes, thereby creating an axial electric field that isproductive of a force retarding motion of the charges in the downstreamdirection. Such retarding force adds to the axial field in the convertersection and thereby increases the energy which must be exerted by thefluid in order to move the particles downstream to the collectorsection. Moreover, if the space charge density immediately downstream ofthe ionizing electrodes is high, as is desirable for maximum efficiency,the image charges will be drawn out of the attractor electrode toneutralize the space charge. This flow of image charges appears asarcing or dielectric breakdown within the flow channel. On the otherhand, in the structure shown in FIG. 7, the image charges are located inthe dielectric plates 130 so that the electric field lines from thecharges in the fluid stream terminate on the image charges in thedielectric plates. These field lines will therefore always be normal tothe direction of flow and produce no additional retarding force on thedownstream motion of the charged particles.

In HO. 7, the charge concentration in the collector section may beefficiently increased up to the maximum permissible concentration for aradial space charge field just less than the field required fordielectric breakdown of the gas by injecting into the particle-laden gassmaller particles to be charged by the ionizing field in the flowchannels. By properly selecting the size of the injected particles, thecharge acquired by the particles, and therefore their mobility, can becontrolled within permissible limits. These injected particles, whichmay be either liquid or solid, form a charged aerosol which is carrieddownstream by the gas into the collector 138, thereby increasing thecharge concentration in the collector and strengthening the space chargefield. Moreover, these particles are precipitated from the stream alongwith the undesired particles so thatthe gas exiting from the outlet ofthe collector is clean. Means for injecting the aerosol particles isrepresented schematically in FIG. 12 by the series of nozzles 140 whichspray the aerosol particles into the inlet of each flow channel betweenthe attractor electrodes 132a.

THEORY AND DESIGN FOR PREClPlTATOR SYSTEMS It can be shown that thehighest space charge potential, relative to the potential at the surfaceof the collector, appears at the collector axis and is given by thefollowing relation:

v n 5&

The space charge field E, at the surface 138a of the collector isdefined by the following equation:

For any given concentration of particles of known size, therefore, theradius R of the collector 138 is ideally:

2e E, en N amas L12 as, 4 2

The efficiency of collection of charged particles has been derived inthe previously mentioned copending application Ser. No. 477,516, and is:

1+ q/xo where h is given by x e u,

K en N in which u is the gas velocity and K, is particle mobility.

Assuming that percent collection efficiency of charged particles isdesired, the effective length of collector L can be determined. Thus,

K en N Combining expressions (24) and (28), we obtain an expressiongoverning the aspect ratio L /R of the collector section of theprecipitator:

Higher collection efficiencies, of course, can be obtained by designingthe collector section with a larger aspect ratio or, as explainedearlier, by seeding the gaseous stream with submicron size particulatematter, which is easily charged to saturation, for augmenting the spacecharge field.

Since a transverse space charge field is present in the generatorsection (between the dielectric plates as well, some deposition ofcharged particles to the surfaces of the dielectric plates tends to takeplace. For purposes of explanation, we can assume that the velocity u ofthe gas through the generator section should be high enough so that notmore than 5 percent of the charged particles reach the surfaces of thedielectric plates. (it may be remarked that with sufficiently high gasspeeds, these few particles become rapidly reentrained in the flow pathwith very little resultant charge loss.) From expression (26), less than5 percent of the charged particles will be deposited on the surfaces ofthe dielectric plates 130 if From the foregoing, it follows that theratio of the gas velocity :4, in the generator to the velocity u, of thegas in the collector for 90 percent collection efficiency should be uc 2L. 2 (32) Having determined the gas velocity ratio, the totalcrosssectional area of the flow paths defined between the dielectricplates I30 can be determined, since the gas flow rate through thecollector I38 and the radius of the collector have been selected for anygiven maximum particle concentration.

As a design example, we may consider a typical precipitator for removingdust particles having a concentration of about l grains/ft: and a meandiameter of about microns. The average particle concentration at thisdust loading is approximately 2XlO' particles/m It is known that theparticles of any given size can hold only a maximum (saturation) charge.In the present example, taking a realistic assumption that the particlesare charged to 50 percent of saturation, the particle mobility isK,,=l0"m./volt sec. and the number of charges per particle N,=3 l0.

Under the foregoing conditions, the ideal radial dimension R of thecollector (from equation (24)) will be 0.55 meters for 90 percentcollection efficiency in the collector. The value of L may be determinedfrom expression (27) and is calculated to be 0.83 14,. Typically, thevelocity of the gas in the collector is about 5m./sec. (equivalent to aflow rate of l0,0()0 c.f.m.) and, thus, L =4. l 5 m.

The maximum potential ofthe space charge in the collector is found fromexpression (2l) to be approximately 800 KV and the required generatorlength L,, i.e., the length of the dielectric plates 130, is thereforeL,=0.28m. From expression (32), the velocity u, of the gas in thegenerator section flow channels is calculated to be u,=56 m./sec.Knowing the desired velocity of the gas through the flow channels andthe charge concentrations, the number and dimensions ofthe flow channelscan be selected. Generally, this will also involve a consideration ofthe spacing between the corona and collector electrodes 131, 1320 suchthat the required voltage for ionization of the gas is ofa practicablevalue.

PRECIPITATOR COLLECTOR Referring again to FIG. 7, the space charge fieldIf, at downstream locations in the collector 138 can be substantiallyincreased through the use ofa passive central conductive electrode I42which is preferably coaxial with the collector I38. This passiveconductor 142 is suitably supported to have its downstream tip I420exposed to the charges exiting from the flow channels in the generatorsection. The conductor I42 is supported by the radially extending armsI43 attached to the wall of the collector I38 and surrounded by adielectric material layer 144. As the flow of charges begins to build upthe space charge potential at the axis of the collector 138, the inducedelectrical potential P on the conductor I42 also increases, since thetip l42a is exposed to the gas flow.

Ultimately, the potential on the conductor 142 will attain the value ofthe space charge potential in which it is located. This potential, ofcourse, appears throughout the length of the passive conductor so thatthe space charge field downstream of the tip 1420 will be increased bythe electrical field gradient established between the charged conductorI42 and the surface 1380 of the collector. It is also possible to applya supplementary potential to the conductor 1420 from an external source145, and to eliminate the dielectric coating I44, if desired. In eithercase, although the radial space charge field gradient decreases in thedownstream direction as the charges are neutralized at the collectorwall, a minimum electrical field gradient normal to the flow path willstill be present due to the charges on the conductor I42.

IONIZING ELECTRODES OF FIG. 8

FIG. 8 illustrates an alternate arrangement for ionizing the gaseousflow in the flow channel. As shown there, the main flow channel betweenthe dielectric plates I46 is subdivided into two secondary channels I47by an intermediate flow dividing plate I48. Attractor electrodes I49 arepositioned at either side of the main flow channel to be exposed to thefluid flow, and the corona discharge wire electrode 150 is disposedtransversely of the flow path intermediate the attractor electrodes I49in a gap 151 in the flow dividing plate I48. Located downstream of theattractor electrodes 149 in the plate I48 is a second attractorelectrode I53 having surfaces I530, 153!) exposed to the flow in thesecondary channels 147. A high direct current potential, represented bythe battery 154, is applied between the corona wire 150 and the secondattractor electrode I53, and also across a voltage dividingpotentiometer 155. The positionable contact a ofthe potentiometer iscoupled directly to the attractor electrodes I49.

In practice, the positionable contact I551: is set to yield a coronadischarge between the corona wire 150 and each of the attractorelectrodes 149. Since, however, the second attractor electrode I53 is ata higher potential than the electrodes I49, the charges drawn from thecorona electrode 150 by the ionizing potential between it and theattractor electrodes 149 are attracted in the downstream direction to asecond attractor electrode I53. It may also be remarked here that thesecond attractor electrode may be replaced with a thin wire similar tothe corona wire I50, if desired, and the corona electrode may beofdiffcrent form, such as those illustrated in FIG. 3.

With the electrode arrangement of FIG. 8, the axial dimension of theeffective ionizing field, i.e., the region in which ionizing current ispresent, is effectively lengthened by the axial distance between theattractor electrodes I49 and the second attractor electrode 153.Concomitant with this axial extension of the ionizing field is anincreased probability of the entrained particles becoming fully chargeddue to the increased residence time of the particles in the ionizingfield.

It can be proven that the effect length b of the ionizing field betweenthe extremes of the first and second attractor electrodes in a flowchannel of minimum cross-sectional dimension h should be such thatb/hZS. Where the density of the gas in the flow channel is large, thecurrent required for charging the entrained particles to saturation isalso increased. This current can be obtained by increasingproportionately the strength of the ionizing field, the ratio b/hremaining unchanged. Ideally, of course, b/h=3, since by increasing theratio b/h by moving the second attractor electrode 153 downstream, ahigher potential must be applied between this electrode and the coronaelectrode.

IONIZER COOLING In cases where the temperature of the working gas flowis high, cooling of the flow in the precipitators or convertersdiscussed may be accomplished by passing a coolant through the ionizingsection. FIG. 9 represents a partial cross section of a typical ionizingand generator section 92. The section 92 is seen to include dielectricplates 920, each provided with a corona electrode 93, and an attractorelectrode 94, both of the type shown in FIG. 3A. Extending laterally ofand at the interior of the dielectric plates 92a are several coolingpassages 96 through which a suitable coolant, such as water, iscontinuously passed for maintaining the plates 92a at a low temperature.In this manner, a substantial reduction in the temperature of the gasflowing between the plates 92a can be effected, at the same time raisingthe potential energy of the particles charged in the ionizing fieldbetween opposed corona and attractor electrodes 93, 94.

Iclaim:

I. Electrogasdynamic converter apparatus for ionizing a stream of fluidcomprising:

fluid guide means having a inlet and outlet and means for establishingtherebetween a flow path boundary configuration for the stream when thestream is passed therethrough, the boundary configuration having asubstantially elongate cross section;

first electrical discharge electrode means disposed at a side of theflow path so as to be substantially flush with the immediatelydownstream portion of the flow boundary configuration; and

first attractor electrode means disposed at an opposite side of the flowpath so as to be substantially flush with the immediately downstreamportion of the flow boundary configuration in opposed relation to thedischarge electrode means, the discharge and attractor electrode meansextending laterally of the flow path in the direction of boundaryconfiguration elongation and having at least portions thereofelectrically exposed to the flow path to form a fluid ionizing electrodepair;

the discharge and attractor electrode means and the boundaryestablishing means forming a substantially smooth, continuous flow pathto reduce friction losses upon movement of the fluid through theapparatus 2. Apparatus as set forth in claim 1, further comprising:

at least one additional discharge electrode means and at least oneadditional attractor electrode means disposed, respectively, to besubstantially flush with the flow boundary configuration, the additionaldischarge and attractor electrode means being in opposed relation andspaced at a distance downstream from the first discharge and attractorelectrode means to form an additional ionizing electrode pair;

each of the additional electrodes and the boundary establishing meansestablishing a substantially smooth continuous transition therebetweento reduce friction losses resulting from the presence of the additionalelectrodes.

3. Apparatus in accordance with claim 2, further comprising:

collector electrode means downstream of the attractor and dischargeelectrode means and disposed in relation to the flow path to collections from the fluid stream; and

a voltage divider network in the form of a resistive film superposed ona surface of the guide means, the network being electrically connectedbetween the collector electrode means and at least one electrode pair todevelop an ionizing potential therebetween.

4. Apparatus as set forth in claim 2, wherein consecutive dischargeelectrodes and consecutive attractor electrodes are located at oppositesides of the flow path from preceding discharge electrodes and attractorelectrodes, respectively.

5. Apparatus as defined in claim 4 in which each associated pair ofdischarge and attractor electrodes and a distance of the flow paththerefrom to a consecutive electrode form an electrogasdynamic converterstage, the apparatus further comprising:

source means connected to alternate electrode pairs for ionizing thefluid to produce ions of opposite electrical polarity in consecutivestages;

means for connecting one side of an external circuit to the dischargeelectrode means at one side of the flow path; and

means for connecting the other side of the external circuit to thedischarge electrodes at the other side of the flow path.

6. Apparatus as defined in claim 1, in which:

said boundary configuration establishing means comprises meansincreasing the cross section of the boundary configuration progressivelyin the area between the inlet and the outlet ofthe fluid guide means toprevent constriction of the stream by electrically produced forcesthereon.

7. Apparatus in accordance with claim 6 wherein:

the transverse dimension of the boundary configuration is substantiallyconstant.

8. Apparatus in accordance with claim 7 wherein:

the constant dimension is greater than approximately 1 millimeter andless than approximately millimeters.

9. Apparatus as defined in claim I wherein the discharge electrode meanscomprises a thin wire; and the thin wire is partially embedded in thefluid guide means to leave only a portion ofthe surface exposed to theflow path.

10. Apparatus in accordance with claim 1 wherein the discharge electrodemeans comprises:

a narrow, thin-film conductive strip superposed on an inside surface ofthe guide means and presenting to the flow path a line of coronadischarge when an ionizing potential, relative to the attractorelectrode means, is applied thereto.

11. Apparatus in accordance with claim 1 wherein the discharge meanscomprises:

a thin strip of conductive material disposed transversely in the guidemeans to leave exposed to the flow path an edge substantially flush withthe flow boundary configuration and forming a line of corona dischargewhen a ionizing potential, relative to the attractor electrode, isapplied thereto.

12. Apparatus according to claim l,further comprising:

plural electroconductive electrical field shielding means forsubstantially reducing the effect of electrical fields adjacent the flowpath boundary;

the shielding means extending laterally of the flow path and includingelectroconductive elements mutually spaced along the axis of flowdownstream of the electrode means; and

means for establishing a conductive path interconnecting theelectroconductive elements.

13. Apparatus according to claim 12 in which:

the electroconductive shielding means comprises conductive elementsdisposed to be surrounded by the stream, each element being spacedsufficiently closely to an adjacent such element to establish a thinboundary layer of fluid when said stream is passed therethrough atsubsonic flow conditions, thereby establishing a part of said flowboundary.

14. Apparatus for ionizing a stream of fluid comprising:

fluid guide means having an inlet and outlet and defining therebetween aflow path for the fluid, the interior of the guide means having adielectric surface providing a flow boundary configuration;

corona discharge electrode means extending laterally of and disposed ata side of the flow path, the corona discharge electrode means comprisinga narrow thin-film strip of conductive ceramic material superposed onthe dielectric surface of the guide means; and

attractor electrode means disposed at an opposite side of the flow pathin opposed relation to the corona discharge electrode means andcomprising a thin-film strip of conductive ceramic material superposedon the dielectric surface, the attractor electrode means beingsubstantially wider than the corona electrode means in the direction offluid flow.

15. Apparatus in accordance with claim 17 wherein:

the ceramic material is selected from the group consisting of zirconiumdiboride, titanium diboride, zirconium carbide, boron carbide, titaniumcarbide, and vanadium carbide.

16. In electrogasdynamic arrangements for effecting an electrogasdynamicenergy exchange, apparatus for ionizing a stream of fluid including thecombination of:

fluid guide means providing a plurality of parallel flow paths for thefluid each having an inlet and an outlet, the fluid guide meansincluding flow separating means defining flow path bounds along which atleast portions thereof are nonconducting so as to avoid a continuousconductive surface adjacent the flow paths for establishing plural flowpaths of elongate cross section in fluid flow areas free of discharge,attractor, and collector electrodes;

electrical discharge electrode means at an upstream end of each flowpath having a charge emitting surface exposed to the flow path torelease an electrical discharge of one polarity thereinto; and

attractor electrode means at the upstream end of each flow path disposedto have a surface thereof exposed to the flow path, each attractorelectrode means forming with a respective discharge electrode means anionizing electrode pair to create therebetween an electrical dischargefield for ionizing the fluid.

17. Apparatus as defined in claim 16 in which:

the flow separating means includes a plurality of spaced, generallyparallel dielectric plates, with the spaces between adjacent onesthereof forming fluid flow channels.

18. Apparatus as defined in claim 16, in which:

the flow separating means includes a plurality ofelectroconductiveelements exposed to the flow and mutually spaced in the direction offlow.

19. Apparatus according to claim 18, further comprising:

means for interconnecting the electroconductive elements through acircuit to establish potential differences between at least two of suchelements.

20. Apparatus according to claim 18, in which:

the electroconductive elements extend laterally of the flow in aplurality of transversely spaced rows.

21. Apparatus according to claim 20, in which:

the electroconductive elements of adjacent rows are axially spaced.

22. Apparatus according to claim 21, further comprising:

circuit means interconnecting the electroconductive elements of adjacentrows to establish on axially consecutive ones thereof progressivelydifferent electrical potentials effective to limit the electrical spacecharge field in the flow paths.

23. Apparatus as defined in claim 16, further comprising:

a collecting chamber disposed to receive ionized fluid flow from theoutlets of the flow paths and defining a further boundary configurationfor the stream, the further boundary configuration having across-sectional area normal to the flow which is greater than thecombined corresponding cross-sectional areas of the flow paths.

24. Apparatus as set forth in claim 23, in which:

the collecting chamber has a conductive surface at the boundary of theflow and exposed to the fluid from the flow channel outlets.

25. Apparatus as defined in claim 23, wherein:

the axial dimension of the flow separating means between the ionizingelectrode pairs and the outlets of the flow channels is at least asgreat as one-half the shortest dimension of the collecting chambernormal to the axis of fluid flow.

26. Apparatus as defined in claim 23, in which the collecting chamber isa conduit in which the ionized flow produces a space charge field, theapparatus further comprising:

passive conductor means associated with and electrically isolated fromthe conduit and operable in the space charge field for enhancing thespace charge field electrical gradient normal to the conduit axis atdownstream locations in the conduit.

27. Apparatus in accordance with claim 16, in which:

the attractor electrode means comprises a pair of conductive platesextending axially of the flow path from the upstream end of the fluidguide means to form the inlet to the fluid guide means, and

the electrical discharge electrode means comprises a thin wirelikeelement disposed between the attractor electrode plates.

28. Apparatus as defined in claim 16, in which:

at least one of the electrical discharge and attractor electrode meansforms an axial extension of the fluid guide means in the upstreamdirection ofthe flow path, and

the cross-sectional area normal to the flow path of the boundaryconfiguration defined by the extension is greater than thecross-sectional area of the boundary configuration defined by the boundsdefining means downstream thereof.

29. Apparatus according to claim 16, in which:

both the attractor and discharge electrode means have a surface thereofsubstantially flush with the flow path boundary and extending in thedirection of flow path boundary elongation, the discharge and attractorelectrodes being disposed at opposite sides of the flow path.

30. Apparatus according to claim 16, further comprising second attractorelectrode means having a conductive surface exposed to the flow path andbeing effective on the electrical discharge to extend the dimension ofthe discharge field in the direction of the axis of fluid flow.

31. Apparatus according to claim 30, in which:

the first attractor electrode means includes conductive surfaces exposedto the flow path at respective opposite sides thereof, and

the second attractor electrode means also includes at least oneconductive surface located in the flow path intermediate the respectiveopposite sides ofthe flow path axially spaced from the first attractorelectrode.

32. Apparatus according to claim 16, further comprising: '5 collectorelectrode means downstream of the electrical discharge and attractorelectrode means; and means for connecting the collector electrode meansto an electrical load to receive from the collector electrode electricalcharges carried by the flow.

2 33. Electrogasdynamic apparatus for ionizing a stream of fluidcomprising:

fluid guide means having an inlet and an outlet and providingtherebetween a channel in the stream; means in the guide means defininga plurality of parallel 25 flow paths for the stream, the flow pathshaving a substantially rectangular boundary configuration of which thecross-sectional area progressively increases from the inlet to theoutlet of the guide means;

corona discharge electrode means extending laterally of and disposed ata side of each of the flow paths; and

attractor electrode means disposed at an opposite side of each of theflow paths in opposed relation to the respective corona dischargeelectrode means, the corona discharge and attractor electrode meanshaving at least portions thereof electrically exposed to the flow path,the corona discharge and attractor electrode means of each flow pathbeing electrically connected, respectively, to the corresponding coronadischarge and attractor electrode means of the other flow paths;

the increase in cross-sectional area of the flow paths followingassociated corona and attractor electrode means being effective toreduce the tendency toward ion acceleration following charging ofthestream.

34. Apparatus in accordance with claim 33, in which the means definingthe plurality of flow paths is a plurality of generally paralleldielectric plates.

35. Apparatus as set forth in claim 33 in which the means defining theplurality of flow paths comprises:

a plurality of layers of elongated wirelike electroconductive elementsextending laterally of the flow paths to provide said boundaryconfiguration.

36. Apparatus in accordance with claim 35, in which theelectroconductive elements are dielectrically coated.

37. Apparatus in accordance with claim 33 wherein:

each of the flow paths has approximately the same transverse dimension.38. Apparatus in accordance with claim 33, further comprising:

collector electrode means downstream of the attractor and coronadischarge electrode means and disposed laterally and at the side of eachof the respective flow paths, the collector electrode means having anelectrical characteristic to neutralize ions in the fluid stream.

39. Electrogasdynamic apparatus operative on a stream of fluid to effecta conversion between the energy of the fluid and electrical energy,comprising:

fluid guide means having an inlet and an outlet and providingtherebetween a channel for the stream;

a plurality of spaced-apart, substantially parallel dielectric plates inthe guide means defining a plurality of parallel flow paths for thefluid;

the flow paths having a substantially rectangular boundary configurationof which the cross-sectional area progressively increases from the inletand to the outlet;

KII

a plurality of elongate corona discharge electrodes disposed laterallyof and at a side of each of the flow paths, the corona dischargeelectrodes being spaced apart in the direction of fluid flow; and

a plurality ofelongate attractor electrodes disposed laterally of and atan opposite side of the respective flow paths in opposed relation to andpaired with the respective corona discharge electrodes, the severalcorona discharge and attractor electrodes providing conductive portionssubstantially flush with the respective surfaces of the dielectricplates so as to be electrically exposed to the flow paths.

40. Apparatus for ionizing a stream of fluid, comprising:

fluid guide means having an inlet and means for establishingtherebetween a flow path boundary configuration for the fluid stream;

electrical discharge electrode means downstream of the fluid guide meansinlet and having a charge-emitting surface exposed to the flow path torelease an electrical discharge, thereinto;

first attractor electrode means disposed to have at least one surfacethereof exposed to the flow path to form with the discharge electrodemeans a first ionizing electrode pair for creating an electrical spacecharge field downstream thereof; and

second attractor electrode means associated with the discharge electrodemeans and having at least one conductive surface disposed in the path offlow, the second attractor electrode means being effective on theelectrical discharge to extend the dimension of the ionizing field inthe direction offluid flow.

4]. Apparatus as set forth in claim 40, in which:

the conductive surface of the second attractor electrode means islocated downstream of the first attractor electrode means.

42. Apparatus as defined in claim 40, in which:

the upstream attractor electrode means includes a pair of conductivesurfaces located at respective opposite sides of the flow path, and

the conductive surface of the second attractor electrode means isdisposed intermediate the respective opposite sides of the flow path.

43. Apparatus as defined in claim 40, further comprising:

dielectric divider means for supporting the second attractor electrodemeans and dividing the flow in the guide means into two separateparallel fluid streams, the second attractor electrode means including asurface exposed to each of the parallel fluid streams.

44. Apparatus as defined in claim 40 further comprising:

means for applying an electrical potential, relative to the electricaldischarge means, to the first attractor electrode means sufficient toeffect ionization of the fluid stream, and

means for applying an electrical potential of the same polarity to thesecond attractor electrode means of greater magnitude than the potentialapplied to the first attractor electrode means to attract ions in theflow path axially thereto.

45. ln electrogasdynamic apparatus for ionizing a stream of fluid guidemeans having an inlet and an outlet and including a pair of spaceddielectric members defining therebetween an elongate flow boundaryconfiguration;

attractor electrode means including a conductive surface extending inthe upstream direction from the upstream ends of the dielectric membersto form therebetween the inlet for the fluid guide means, the inletbeing of an enlarged cross-sectional area normal to the flow path andconverging to a smaller cross-sectional area of the flow pathimmediately adjacent thereto; and

electrical discharge electrode means associated with the attractorelectrode means and forming therewith an ionizing electrode pair forsubjecting the fluid stream at the inlet to an electrical dischargefield.

46. Apparatus according to claim 45, in which:

the discharge electrode means comprises a plurality of spaced apartthin, wirelike elements, arranged in a plane substantially parallel tothe fluid stream and intermediate the conductive surfaces oftheattractor electrode means.

47. Electrogasdynamic apparatus for operating on a stream offluid,comprising: I

means defining a flow path for the fluid having an inlet and an outlet;

means for ionizing the fluid in an upstream portion of the flow path tocreate a space charge field downstream thereof;

a conduit disposed to receive the ionized fluid from the outlet of theflow path defining means and thereby to have a space charge field in theinterior thereof for collecting the electrical charges carried by thefluid, fluid guide means for defining a substantially nonconductingboundary portion intermediate the ionizing and collecting means; and

passive conductor means associated with and electrically isolated fromthe conduit and operable in the space charge field for enhancing thespace charge field electrical gradient normal to the conduit axis atdownstream locations in the conduit.

48. Apparatus in accordance with claim 47, in which:

the conductor is elongated in the direction of fluid flow and has asubstantial downstream portion electrically insulated from the flow,with at least an upstream portion exposed to the flow to be energized bythe charges carried by the fluid.

49. Apparatus as defined in claim 48, wherein: the conductor is coaxialwith the conduit.

50. Apparatus as defined in claim 47, further comprising:

means for applying to the passive conductor means an electricalpotential to establish between the passive conductor and pointssurrounding it an electrical field transverse of the direction of flow.

51. An electrogasdynamic apparatus for operating on a stream of gascomprising:

an enclosure having an inlet and an outlet for the stream;

electrical discharge electrode means at an upstream location in theenclosure for injecting electrical charges into the stream; and

a plurality of electroconductive elements extending interiorly of theenclosure, transversely of and in the flow of downstream of theelectrical discharge means, and being mutually spaced in the directionof flow;

the enclosure being free of other charging, attracting, and chargecollecting electrodes in the enclosure portion housing the conductiveelements; and

means for connecting the electroconductive elements to an electricalcircuit to establish on each thereof a reference potential to modify theelectric field within the enclosure.

52. Apparatus according to claim 51, in which:

the electroconductive elements are disposed in at least one planeparallel to the direction of flow between the inlet and outlet of theenclosure and intermediate sides of the enclosure.

53. Apparatus according to claim 51, in which:

the electroconductive elements are disposed in at least two spacedplanes parallel to the direction of flow between the inlet and outlet ofthe enclosure.

54. Apparatus according to claim 51, in which:

the electroconductive elements comprise a plurality of conductors havinga maximum cross-sectional dimension substantially less than the smallestcross-sectional dimension of any flow path for the stream within theenclosure.

55. Apparatus according to claim 51, in which:

the reference potential on electroconductive elements at a given axiallocation differs from the reference potential on electroconductiveelements at a different axial location.

56. Apparatus according to claim 51, further comprising:

collector electrode means exposed to the stream downstream of theelectroconductive elements and means for connecting the collectorelectrode to an external electrical circuit.

57. Apparatus according to claim in which:

the electrical circuit comprises a resistive film on the enclosure, and

the axially displaced ele-z'troconductive elements are electricallyconnected to points along the resistive film to connect an impedancebetween the axially displaced elements.

58. An electrogasdynamic apparatus for operating on a stream of gas,comprising:

means defining an enclosure having an inlet and outlet for the stream;

electrical discharge means at an upstream location in the enclosure forinjecting electrical charges into the stream; and

an array of electroconductive shielding elements disposed in the streamat a downstream location for establishing a reference potential at eachthereof effective to limit the maximum space charge field between theelectrical discharge means and the outlet by shielding sections of theenclosure from electrical charge concentrations in the stream at othersections of the enclosure.

59. In apparatus for ionizing a gaseous stream:

guide means including a pair of parallel, spaced-apart dielectric platesdefining therebetween a flow channel for the stream of gas and having aninlet and an outlet; and

ionizing electrode means at an upstream location in the guide means forcreating an electrical discharge field in the flow channel, thedischarge field being effective to produce mobile charge carriers to beforced downstream by the stream;

the dielectric plates having passages therein unexposed to the streamfor directing a coolant therethrough to effect a transfer of heat fromthe stream and to the plates downstream of the electrical dischargefield.

60. In an electrogasdynamic device, defining an axial flow path for astream of gas carrying electrical charges, the improvement comprising:

an outer, axially elongate channel member for passage of the gastherethrough,

means for establishing the electrical charges carried by the gas throughthe channel,

means for controlling the electric field distribution across theinterior of the channel member downstream from the charge establishingmeans,

the field controlling means including an array of axially spacedelectroconductive shielding elements within the channel member anddisposed in the stream to extend thereacross removed from the means forestablishing the electrical charges, and

means, connected with the shielding elements, for establishing onaxially spaced elements a different electrical potential to control theaxial electric field gradient within the channel member. 61. Theimprovement according to claim 60, in which: at least some of theelements are mutually spaced transversely of the flow path.

62. The improvement according to claim 60, in which:

the electroconductive elements present conductive surfaces to the gasstream and are electrically connected to drain off charges, therebyreducing excessive electrical charge buildup within the channel.

63. The improvement of claim 62, in which: the elements comprise metalrodlike members.

1. Electrogasdynamic converter apparatus for ionizing a stream of fluidcomprising: fluid guide means having a inlet and outlet and means forestablishing therebetween a flow path boundary configuration for thestream when the stream is passed therethrough, the boundaryconfiguration having a substantially elongate cross section; firstelectrical discharge electrode means disposed at a side of the flow pathso as to be substantially flush with the immediately downstream portionof the flow boundary configuration; and first attractor electrode meansdisposed at an opposite side of the flow path so as to be substantiallyflush with the immediately downstream portion of the flow boundaryconfiguration in opposed relation to the discharge electrode means, thedischarge and attractor electrode means extending laterally of the flowpath in the direction of boundary configuration elongation and having atleast portions thereof electrically exposed to the flow path to form afluid ionizing electrode pair; the discharge and attractor electrodemeans and the boundary establishing means forming a substantiallysmooth, continuous flow path to reduce friction losses upon movement ofthe fluid through the apparatus
 2. Apparatus as set forth in claim 1,further comprising: at least one additional discharge electrode meansand at least one additional attractor electrode means disposed,respectively, to be substantially flush with the flow boundaryconfiguration, the additional discharge and attractor electrode meansbeing in opposed relation and spaced at a distance downstream from thefirst discharge and attractor electrode means to form an additionalionizing electrode pair; each of the additional electrodes and theboundary establishing means establishing a substantially smoothcontinuous transition therebetween to reduce friction losses resultingfrom the presence of the additional electrodes.
 3. Apparatus inaccordance with claim 2, further comprising: collector electrode meansdownstream of the attractor and discharge electrode means and disposedin relation to the flow path to collect ions from the fluid stream; anda voltage divider network in the form of a resistive film superposed ona surface of the guide means, the network being electrically connectedbetween the collector electrode means and at least one electrode pair todevelop an ionizing potential therebetween.
 4. Apparatus as set forth inclaim 2, wherein consecutive discharge electrodes and consecutiveattractor electrodes are located at opposite sides of the flow path frompreceding discharge electrodes and attractor electrodes, respectively.5. Apparatus as defined in claim 4 in which each associated pair ofdischarge and attractor electrodes and a distance of the flow paththerefrom to a consecutive electrode form an electrogasdynamic converterstage, the apparatus further comprising: source means connected toalternate electrode pairs for ionizing the fluid to produce ions ofopposite electrical polarity in consecutive stages; means for connectingone side of an external circuit to the discharge electrode means at oneside of the flow path; and means for connecting the other side of theexternal circuit to the discharge electrodes at the other side of theflow path.
 6. Apparatus as defined in claim 1, in which: said boundaryconfiguration establishing means comprises means increasing the crosssection of the boundary configuration progressively in the area betweenthe inlet and the outlet of the fluid guide means to preventconstriction of the stream by electrically produced forces thereon. 7.Apparatus in accordance with claim 6 wherein: the transverse dimensionof the boundary configuration is substantially constant.
 8. Apparatus inaccordance with claim 7 wherein: the constant dimension is greater thanapproximately 1 millimeter and less than approximately 5 millimeters. 9.Apparatus as defined in claim 1 wherein the discharge electrode meanscomprises a thin wire; and the thin wire is partially embedded in thefluid guide means to leave only a portion of the surface exposed to theflow path.
 10. Apparatus in accordance with claim 1 wherein thedischarge electrode means comprises: a narrow, thin-film conductivestrip superposed on an inside surface of the guide means and presentingto the flow path a line of corona discharge when an ionizing potential,relative to the attractor electrode means, is applied thereto. 11.Apparatus in accordance with claim 1 wherein the discharge meanscomprises: a thin strip of conductive material disposed transversely inthe guide means to leave exposed to the flow path an edge substantiallyflush with the flow boundary configuration and forming a line of coronadischarge when a ionizing potential, relative to the attractorelectrode, is applied thereto.
 12. Apparatus according to claim 1,further comprising: plural electroconductive electrical field shieldingmeans for substantially reducing the effect of electrical fieldsadjacent the flow path boundary; the shielding means extending laterallyof the flow path and including electroconductive elements mutuallyspaced along the axis of flow downstream of the electrode means; andmeans for establishing a conductive path interconnecting theelectroconductive elements.
 13. Apparatus according to claim 12 inwhich: the electroconductive shielding means comprises conductiveelements disposed to be surrounded by the stream, each element beingspaced sufficiently closely to an adjacent such element to establish athin boundary layer of fluid when said stream is passed therethrough atsubsonic flow conditions, thereby establishing a part of said flowboundary.
 14. Apparatus for ionizing a stream of fluid comprising: fluidguide means having an inlet and outlet and defining therebetween a flowpath for the fluid, the interior of the guide means having a dielectricsurface providing a flow boundary configuration; corona dischargeelectrode means extending lateRally of and disposed at a side of theflow path, the corona discharge electrode means comprising a narrowthin-film strip of conductive ceramic material superposed on thedielectric surface of the guide means; and attractor electrode meansdisposed at an opposite side of the flow path in opposed relation to thecorona discharge electrode means and comprising a thin-film strip ofconductive ceramic material superposed on the dielectric surface, theattractor electrode means being substantially wider than the coronaelectrode means in the direction of fluid flow.
 15. Apparatus inaccordance with claim 17 wherein: the ceramic material is selected fromthe group consisting of zirconium diboride, titanium diboride, zirconiumcarbide, boron carbide, titanium carbide, and vanadium carbide.
 16. Inelectrogasdynamic arrangements for effecting an electrogasdynamic energyexchange, apparatus for ionizing a stream of fluid including thecombination of: fluid guide means providing a plurality of parallel flowpaths for the fluid each having an inlet and an outlet, the fluid guidemeans including flow separating means defining flow path bounds alongwhich at least portions thereof are nonconducting so as to avoid acontinuous conductive surface adjacent the flow paths for establishingplural flow paths of elongate cross section in fluid flow areas free ofdischarge, attractor, and collector electrodes; electrical dischargeelectrode means at an upstream end of each flow path having a chargeemitting surface exposed to the flow path to release an electricaldischarge of one polarity thereinto; and attractor electrode means atthe upstream end of each flow path disposed to have a surface thereofexposed to the flow path, each attractor electrode means forming with arespective discharge electrode means an ionizing electrode pair tocreate therebetween an electrical discharge field for ionizing thefluid.
 17. Apparatus as defined in claim 16 in which: the flowseparating means includes a plurality of spaced, generally paralleldielectric plates, with the spaces between adjacent ones thereof formingfluid flow channels.
 18. Apparatus as defined in claim 16, in which: theflow separating means includes a plurality of electroconductive elementsexposed to the flow and mutually spaced in the direction of flow. 19.Apparatus according to claim 18, further comprising: means forinterconnecting the electroconductive elements through a circuit toestablish potential differences between at least two of such elements.20. Apparatus according to claim 18, in which: the electroconductiveelements extend laterally of the flow in a plurality of transverselyspaced rows.
 21. Apparatus according to claim 20, in which: theelectroconductive elements of adjacent rows are axially spaced. 22.Apparatus according to claim 21, further comprising: circuit meansinterconnecting the electroconductive elements of adjacent rows toestablish on axially consecutive ones thereof progressively differentelectrical potentials effective to limit the electrical space chargefield in the flow paths.
 23. Apparatus as defined in claim 16, furthercomprising: a collecting chamber disposed to receive ionized fluid flowfrom the outlets of the flow paths and defining a further boundaryconfiguration for the stream, the further boundary configuration havinga cross-sectional area normal to the flow which is greater than thecombined corresponding cross-sectional areas of the flow paths. 24.Apparatus as set forth in claim 23, in which: the collecting chamber hasa conductive surface at the boundary of the flow and exposed to thefluid from the flow channel outlets.
 25. Apparatus as defined in claim23, wherein: the axial dimension of the flow separating means betweenthe ionizing electrode pairs and the outlets of the flow channels is atleast as great as one-half the shortest dimension of the collectingchamber normal to the axiS of fluid flow.
 26. Apparatus as defined inclaim 23, in which the collecting chamber is a conduit in which theionized flow produces a space charge field, the apparatus furthercomprising: passive conductor means associated with and electricallyisolated from the conduit and operable in the space charge field forenhancing the space charge field electrical gradient normal to theconduit axis at downstream locations in the conduit.
 27. Apparatus inaccordance with claim 16, in which: the attractor electrode meanscomprises a pair of conductive plates extending axially of the flow pathfrom the upstream end of the fluid guide means to form the inlet to thefluid guide means, and the electrical discharge electrode meanscomprises a thin wirelike element disposed between the attractorelectrode plates.
 28. Apparatus as defined in claim 16, in which: atleast one of the electrical discharge and attractor electrode meansforms an axial extension of the fluid guide means in the upstreamdirection of the flow path, and the cross-sectional area normal to theflow path of the boundary configuration defined by the extension isgreater than the cross-sectional area of the boundary configurationdefined by the bounds defining means downstream thereof.
 29. Apparatusaccording to claim 16, in which: both the attractor and dischargeelectrode means have a surface thereof substantially flush with the flowpath boundary and extending in the direction of flow path boundaryelongation, the discharge and attractor electrodes being disposed atopposite sides of the flow path.
 30. Apparatus according to claim 16,further comprising: second attractor electrode means having a conductivesurface exposed to the flow path and being effective on the electricaldischarge to extend the dimension of the discharge field in thedirection of the axis of fluid flow.
 31. Apparatus according to claim30, in which: the first attractor electrode means includes conductivesurfaces exposed to the flow path at respective opposite sides thereof,and the second attractor electrode means also includes at least oneconductive surface located in the flow path intermediate the respectiveopposite sides of the flow path axially spaced from the first attractorelectrode.
 32. Apparatus according to claim 16, further comprising:collector electrode means downstream of the electrical discharge andattractor electrode means; and means for connecting the collectorelectrode means to an electrical load to receive from the collectorelectrode electrical charges carried by the flow.
 33. Electrogasdynamicapparatus for ionizing a stream of fluid comprising: fluid guide meanshaving an inlet and an outlet and providing therebetween a channel inthe stream; means in the guide means defining a plurality of parallelflow paths for the stream, the flow paths having a substantiallyrectangular boundary configuration of which the cross-sectional areaprogressively increases from the inlet to the outlet of the guide means;corona discharge electrode means extending laterally of and disposed ata side of each of the flow paths; and attractor electrode means disposedat an opposite side of each of the flow paths in opposed relation to therespective corona discharge electrode means, the corona discharge andattractor electrode means having at least portions thereof electricallyexposed to the flow path, the corona discharge and attractor electrodemeans of each flow path being electrically connected, respectively, tothe corresponding corona discharge and attractor electrode means of theother flow paths; the increase in cross-sectional area of the flow pathsfollowing associated corona and attractor electrode means beingeffective to reduce the tendency toward ion acceleration followingcharging of the stream.
 34. Apparatus in accordance with claim 33, inwhich the means defining the plurality of flow paths is a plurality ofgenErally parallel dielectric plates.
 35. Apparatus as set forth inclaim 33 in which the means defining the plurality of flow pathscomprises: a plurality of layers of elongated wirelike electroconductiveelements extending laterally of the flow paths to provide said boundaryconfiguration.
 36. Apparatus in accordance with claim 35, in which theelectroconductive elements are dielectrically coated.
 37. Apparatus inaccordance with claim 33 wherein: each of the flow paths hasapproximately the same transverse dimension.
 38. Apparatus in accordancewith claim 33, further comprising: collector electrode means downstreamof the attractor and corona discharge electrode means and disposedlaterally and at the side of each of the respective flow paths, thecollector electrode means having an electrical characteristic toneutralize ions in the fluid stream.
 39. Electrogasdynamic apparatusoperative on a stream of fluid to effect a conversion between the energyof the fluid and electrical energy, comprising: fluid guide means havingan inlet and an outlet and providing therebetween a channel for thestream; a plurality of spaced-apart, substantially parallel dielectricplates in the guide means defining a plurality of parallel flow pathsfor the fluid; the flow paths having a substantially rectangularboundary configuration of which the cross-sectional area progressivelyincreases from the inlet and to the outlet; a plurality of elongatecorona discharge electrodes disposed laterally of and at a side of eachof the flow paths, the corona discharge electrodes being spaced apart inthe direction of fluid flow; and a plurality of elongate attractorelectrodes disposed laterally of and at an opposite side of therespective flow paths in opposed relation to and paired with therespective corona discharge electrodes, the several corona discharge andattractor electrodes providing conductive portions substantially flushwith the respective surfaces of the dielectric plates so as to beelectrically exposed to the flow paths.
 40. Apparatus for ionizing astream of fluid, comprising: fluid guide means having an inlet and meansfor establishing therebetween a flow path boundary configuration for thefluid stream; electrical discharge electrode means downstream of thefluid guide means inlet and having a charge-emitting surface exposed tothe flow path to release an electrical discharge, thereinto; firstattractor electrode means disposed to have at least one surface thereofexposed to the flow path to form with the discharge electrode means afirst ionizing electrode pair for creating an electrical space chargefield downstream thereof; and second attractor electrode meansassociated with the discharge electrode means and having at least oneconductive surface disposed in the path of flow, the second attractorelectrode means being effective on the electrical discharge to extendthe dimension of the ionizing field in the direction of fluid flow. 41.Apparatus as set forth in claim 40, in which: the conductive surface ofthe second attractor electrode means is located downstream of the firstattractor electrode means.
 42. Apparatus as defined in claim 40, inwhich: the upstream attractor electrode means includes a pair ofconductive surfaces located at respective opposite sides of the flowpath, and the conductive surface of the second attractor electrode meansis disposed intermediate the respective opposite sides of the flow path.43. Apparatus as defined in claim 40, further comprising: dielectricdivider means for supporting the second attractor electrode means anddividing the flow in the guide means into two separate parallel fluidstreams, the second attractor electrode means including a surfaceexposed to each of the parallel fluid streams.
 44. Apparatus as definedin claim 40 further comprising: means for applying an electricalpotential, relative to the electrical discharge Means, to the firstattractor electrode means sufficient to effect ionization of the fluidstream, and means for applying an electrical potential of the samepolarity to the second attractor electrode means of greater magnitudethan the potential applied to the first attractor electrode means toattract ions in the flow path axially thereto.
 45. In electrogasdynamicapparatus for ionizing a stream of fluid: fluid guide means having aninlet and an outlet and including a pair of spaced dielectric membersdefining therebetween an elongate flow boundary configuration; attractorelectrode means including a conductive surface extending in the upstreamdirection from the upstream ends of the dielectric members to formtherebetween the inlet for the fluid guide means, the inlet being of anenlarged cross-sectional area normal to the flow path and converging toa smaller cross-sectional area of the flow path immediately adjacentthereto; and electrical discharge electrode means associated with theattractor electrode means and forming therewith an ionizing electrodepair for subjecting the fluid stream at the inlet to an electricaldischarge field.
 46. Apparatus according to claim 45, in which: thedischarge electrode means comprises a plurality of spaced apart thin,wirelike elements, arranged in a plane substantially parallel to thefluid stream and intermediate the conductive surfaces of the attractorelectrode means.
 47. Electrogasdynamic apparatus for operating on astream of fluid, comprising: means defining a flow path for the fluidhaving an inlet and an outlet; means for ionizing the fluid in anupstream portion of the flow path to create a space charge fielddownstream thereof; a conduit disposed to receive the ionized fluid fromthe outlet of the flow path defining means and thereby to have a spacecharge field in the interior thereof for collecting the electricalcharges carried by the fluid, fluid guide means for defining asubstantially nonconducting boundary portion intermediate the ionizingand collecting means; and passive conductor means associated with andelectrically isolated from the conduit and operable in the space chargefield for enhancing the space charge field electrical gradient normal tothe conduit axis at downstream locations in the conduit.
 48. Apparatusin accordance with claim 47, in which: the conductor is elongated in thedirection of fluid flow and has a substantial downstream portionelectrically insulated from the flow, with at least an upstream portionexposed to the flow to be energized by the charges carried by the fluid.49. Apparatus as defined in claim 48, wherein: the conductor is coaxialwith the conduit.
 50. Apparatus as defined in claim 47, furthercomprising: means for applying to the passive conductor means anelectrical potential to establish between the passive conductor andpoints surrounding it an electrical field transverse of the direction offlow.
 51. An electrogasdynamic apparatus for operating on a stream ofgas comprising: an enclosure having an inlet and an outlet for thestream; electrical discharge electrode means at an upstream location inthe enclosure for injecting electrical charges into the stream; and aplurality of electroconductive elements extending interiorly of theenclosure, transversely of and in the flow of downstream of theelectrical discharge means, and being mutually spaced in the directionof flow; the enclosure being free of other charging, attracting, andcharge collecting electrodes in the enclosure portion housing theconductive elements; and means for connecting the electroconductiveelements to an electrical circuit to establish on each thereof areference potential to modify the electric field within the enclosure.52. Apparatus according to claim 51, in which: the electroconductiveelements are disposed in at least one plane parallel to the direction offlow between the inlet and outleT of the enclosure and intermediatesides of the enclosure.
 53. Apparatus according to claim 51, in which:the electroconductive elements are disposed in at least two spacedplanes parallel to the direction of flow between the inlet and outlet ofthe enclosure.
 54. Apparatus according to claim 51, in which: theelectroconductive elements comprise a plurality of conductors having amaximum cross-sectional dimension substantially less than the smallestcross-sectional dimension of any flow path for the stream within theenclosure.
 55. Apparatus according to claim 51, in which: the referencepotential on electroconductive elements at a given axial locationdiffers from the reference potential on electroconductive elements at adifferent axial location.
 56. Apparatus according to claim 51, furthercomprising: collector electrode means exposed to the stream downstreamof the electroconductive elements and means for connecting the collectorelectrode to an external electrical circuit.
 57. Apparatus according toclaim 51, in which: the electrical circuit comprises a resistive film onthe enclosure, and the axially displaced electroconductive elements areelectrically connected to points along the resistive film to connect animpedance between the axially displaced elements.
 58. Anelectrogasdynamic apparatus for operating on a stream of gas,comprising: means defining an enclosure having an inlet and outlet forthe stream; electrical discharge means at an upstream location in theenclosure for injecting electrical charges into the stream; and an arrayof electroconductive shielding elements disposed in the stream at adownstream location for establishing a reference potential at eachthereof effective to limit the maximum space charge field between theelectrical discharge means and the outlet by shielding sections of theenclosure from electrical charge concentrations in the stream at othersections of the enclosure.
 59. In apparatus for ionizing a gaseousstream: guide means including a pair of parallel, spaced-apartdielectric plates defining therebetween a flow channel for the stream ofgas and having an inlet and an outlet; and ionizing electrode means atan upstream location in the guide means for creating an electricaldischarge field in the flow channel, the discharge field being effectiveto produce mobile charge carriers to be forced downstream by the stream;the dielectric plates having passages therein unexposed to the streamfor directing a coolant therethrough to effect a transfer of heat fromthe stream and to the plates downstream of the electrical dischargefield.
 60. In an electrogasdynamic device, defining an axial flow pathfor a stream of gas carrying electrical charges, the improvementcomprising: an outer, axially elongate channel member for passage of thegas therethrough, means for establishing the electrical charges carriedby the gas through the channel, means for controlling the electric fielddistribution across the interior of the channel member downstream fromthe charge establishing means, the field controlling means including anarray of axially spaced electroconductive shielding elements within thechannel member and disposed in the stream to extend thereacross removedfrom the means for establishing the electrical charges, and means,connected with the shielding elements, for establishing on axiallyspaced elements a different electrical potential to control the axialelectric field gradient within the channel member.
 61. The improvementaccording to claim 60, in which: at least some of the elements aremutually spaced transversely of the flow path.
 62. The improvementaccording to claim 60, in which: the electroconductive elements presentconductive surfaces to the gas stream and are electrically connected todrain off charges, thereby reducing excessive electrical charge buildupwithin the channel.
 63. The improvEment of claim 62, in which: theelements comprise metal rodlike members.